1. Field of the Invention
The present invention relates to improvements to devices for drilling branched wells, also known as multiple-completion wells.
2. Description of the Prior Art
It has been the practice for a very long time to drill multiple-completion wells which are none other than branch boreholes obtained from a main or parent well.
An elaborate technique of multiple-borehole drilling consists in making use of deflecting means which are usually made up of three deflecting tubes placed at 120.degree. with respect to each other, in lowering them into the parent well and in fixing them in situ. Coupling means are then employed for selecting one of the deflecting tubes from which it is desired to drill a branch line or lateral branch borehole. Devices for carrying out this technique are described in U.S. Pat. Nos. 4,396,075, 4,415,205 and in French Pat. No. 83 13 981.
At least in the U.S. patents cited above, the devices described entail the need to lower the selecting means together with the drilling packer itself. It is consequently necessary in any operation performed within the main well or within one of the branch boreholes of the well, not only to displace the drilling packer but also to displace the selecting means and consequently all their elements and components. This is the case in particular at the time of a change of packer or of a drilling tool which makes it necessary to withdraw the selecting means, to separate them from the drilling packer and then to re-position them on the new drilling packer to be lowered into the well.
Furthermore, positioning in a branch borehole of tools suspended from cables such as well-logging tools is impossible when using the devices described in the U.S. patents cited earlier. It is in fact impossible to re-enter a predetermined branch borehole unless the boreholes are lined with a casing string which extends to the surface.
The aim of the present invention is to overcome the disadvantages mentioned in the foregoing and to propose a device for drilling branched boreholes in which the drilling packer is dissociated from the selecting means which also have a coupling function in French Pat. No. 83 13981.